1. Field of the Invention
This invention relates to the production of alcohols and more specifically to an improved process for producing alcohols by hydrogenation of aldehydes which have been prepared by an oxo reaction.
2. Description of the Prior Art
The oxo process for preparing oxo alcohols is well kown and in general involves three major stages. In the first stage, hydrogen and carbon monoxide are reacted with an olefin in the presence of a hydroformylation catalyst at elevated temperature and pressure to obtain a hydroformylation reaction effluent containing an aldehyde product having one more carbon than the feed olefin. In the second stage, the hydroformylation reaction effluent is then treated to remove the metal hydroformylation catalyst such as by heating the hydroformylation effluent to convert dissolved cobalt carbonyl catalyst into a form which is insoluble in the liquid effluent, followed by separation of the solids (e.g., by direct deposition on inert packings contained in the thermal demetalling vessel, filtration and other means). In the third stage, the demetalled hydroformylation is subjected to hydrogenation conditions. These hydrogenations generally employ one of two classes of catalysts: (1) high temperature catalysts, such as metallic nickel or cobalt, and sulfactive catalysts such as the sulfides of tungsten, molybdenum and nickel, which are employed at temperatures of from about 275.degree. to 500.degree. F., and (2) low temperature catalysts such as copper chromite (mixture of Cr and Cu oxides) which are used at temperatures of from about 150.degree. to 300.degree. F.
Illustrative of prior art methods for demetalling the hydroformylation reaction mixture is U.S. Pat. No. 2,779,794, in which the effluent from the hydroformylation is heated at a temperature of 250.degree. to 350.degree. F. and a pressure of 100 to 200 psi to convert dissolved cobalt carbonyl into a form which is insoluble in the product aldehyde. The cobalt solids are then removed by settling and the demetalled aldehyde layer is cooled and ultimately passed to hydrogenation. Thermal demetalling methods are also discussed in U.S. Pat. Nos. 2,757,203 (300.degree.-400.degree. F.); 2,809,220 (150.degree.-500.degree. F.); and 2,905,716 (302.degree.-392.degree. F.).
Acetals are formed as by-products during the above process and constitute a yield loss to the desired oxo alcohols. Several methods have been developed to minimize this source of yield loss. In U.S. Pat. No. 2,595,096, the demetalled oxo reactor effluent, which has been demetalled at a temperature of from 200.degree. to 450.degree. F., is subjected to hydrogenation to form a hydrogenation effluent which contains the desired oxo alcohol, unconverted aldehyde, lights, inerts and a substantial portion, up to 50 volume %, acetals.
This stream is subjected to several distillative steps to remove inerts, lights and the alcohol product. The resulting acetal-containing stream is then hydrolyzed (using either dilute mineral acid at 200.degree. to 250.degree. F., or steam at 300.degree. to 400.degree. F.) to liberate additional alcohols and aldehydes for recovery and recycle to the feed line to the hydrogenation reactor.
The process of U.S. Pat. No. 2,757,203 subjects the hydroformylation effluent to a steam distillation in the presence of added mineral acid (such as phosphoric acid) to hydrolyze acetal impurities while simultaneously thermally decomposing the cobalt carbonyl catalyst. The overhead vapors from this distillation step comprise aldehydes, water and carbon monoxide gas (the latter being formed from the cobalt catalyst decomposition). These vapors are partially condensed, the gaseous CO is removed and the aqueous and aldehyde layers are separated, with the aldehyde layer being passed to subsequent hydrogenation. In a second embodiment, the patentee hydrogenates a demetalled hydroformylation effluent and treats the hydrogenation effluent by a series of distillations, the first of which is intended to separate aldehydes as overhead using a steam distillation in the presence of added phosphoric acid again to hydrolyze the acetals in the hydrogenation effluent.
U.S. Pat. No. 2,809,220 discloses a process in which water is added to the hydrogenation zone in which a demetalled hydroformylation effluent is subjected to hydrogenation conditions. The patentee indicates that the advantage of water in the hydrogenation zone is to assist in the breakdown of the secondary reaction products, such as acetals, to form additional alcohol product. However, this process employs a high temperature hydrogenation catalyst operating at from 400.degree. to 600.degree. F.
In U.S. Pat. No. 3,092,670, a demetalled hydroformylation effluent is fractionated with steam under controlled conditions to remove as overhead only unreacted olefins. The remainder of the product, including the acetals, is not separated but is passed to the subsequent hydrogenation stage.
U.S. Pat. No. 2,905,716 discloses another method for purification of a hydroformylation reaction effluent containing cobalt catalyst and acetal impurities.
British Patent No. 715,390 performs concurrent decobalting and acetal hydrolysis in the presence of dilute acid or water at temperatures below about 250.degree. F.